This invention relates to apparatus and methods for shaping tubes and, in particular, to shaping glass tubes intended for use in the manufacture of optic fibers and for doing so semi-automatically or automatically.
One process for the manufacture of optical fibers is referred to as the modified chemical vapor deposition (MCVD) process in which the internal wall of a glass cylinder (also referred to herein as the xe2x80x9cstarter tubexe2x80x9d or xe2x80x9cpreform tubexe2x80x9d) is coated with uniform layers of reactants and gas vapors to form the rod from which optic fibers will be extruded. To ensure the proper and uniform flow of gases within the starter tube, it is desirable to join, or fuse, the starter tube to an exhaust tube prior to initiating the actual fiber optic manufacturing process.
For optimum results the exhaust tube should provide smooth, continuous flow for the gases escaping from the starter tube to, and through, the exhaust tube. To accomplish this result, the exhaust tube must generally have a larger diameter than the starter tube. However, at their interface and mating ends the exhaust tube must mesh smoothly and continuously with the starter tube and must have a profile which aids in the smooth flow of gases out of the starter tube.
It is also noted that each exhaust tube is intended to be joined (or fused) to a starter tube and that the two xe2x80x9ccombinedxe2x80x9d tubes are then operated as a unit. Typically, the combined tubes are mounted in an apparatus in which they are made to rotate for many hours while gases and reactants are being injected into the starter tube under intense heat conditions, for depositing uniform layers to subsequently form optic fibers. To ensure the formation of consistently uniform layers, it is important that the two tubes be aligned very accurately; (i.e., have a common center line) throughout the process.
In presently known systems the end of an exhaust tube designed to mate with a starter tube is shaped manually using a graphite forming tool, or like manual equipment. This process is an xe2x80x9cartxe2x80x9d dependent on the skills and techniques of the artisan shaping the mating end and interface of the exhaust tube. This is undesirable and problematic because tubes shaped manually have little uniformity and dimensional reproducibility. As a result, numerous defective exhaust tubes are produced. Equally problematic is that, even when an exhaust tube is not defective, the mating of an exhaust tube with a starter tube is subject to alignment problems.
Thus, there is a dual problem of uniformly shaping and contouring the end of an exhaust tube so that the starter tube (at its mating output) meshes smoothly with the exhaust tube at their common interface and of aligning the two tubes accurately. Clearly, the requirements placed on the manufacture of fiber optics is very demanding and very costly. It may take many hours to produce a. fiber optic xe2x80x9cpreformxe2x80x9d. Even very small defects, because of their cumulative effect, may result in the loss of much material, energy and time, at great cost to the manufacturer.
Another problem is that in accordance with the prior art when the starter and exhaust tubes are to be joined or fused together, they are cantilevered from spindle chucks. An operator must support the cantilevered tubes by manual means or through the use of a xe2x80x9cjackxe2x80x9d device and raise or lower the rotating starter and exhaust tubes to achieve co-axial alignment with the end of the exhaust tube. Heat is applied at the support point of the starter tube to stress relieve the starter tube as the operator applies a relocating force to the starter and exhaust tubes. The quality of the co-axiality between the two tubes in this butt-splice technique is a function of the operator""s skill. This is undesirable because the quality of the results is not predictable.
Various solutions to the problems of shaping glass tubes are disclosed in Applicants"" co-pending application Ser. No. 09/497,044, filed Feb. 2, 2000, and U.S. Pat. No. 6,536,239. However, in the molding operation disclosed in those applications, the exhaust tube must be heated to a very high temperature by means of a torch until the end region of the tube becomes soft. Then the torch is removed and the mold pieces are applied to the end region of the tube. During this time the torch is removed and until the mold pieces are applied, the end region of the tube. During this time the torch is removed and until the mold is applied, the tube may not have the desired softness. Overheating the tube end to compensate for the ensuing cooling may result in the tube end deforming in an undersired manner. The prior art schemes also require that the torch be moved via a motor or other control means under relatively high temperature conditions.
Applicants"" invention is aimed at reducing the problems associated with the shaping of one end of a hollow cylindrical glass tube (e.g., an exhaust tube).
Known prior art techniques require the application of a torch to the end region of a tube until it reaches a malleable state and then the retraction of the heat source and the application of a mold to shape the end region. In contrast thereto, in accordance with Applicants"" invention, a mold for shaping the end of a tube also includes means for heating the tube. Consequently, the mold serves the dual function of heating the tube and shaping it. This eliminates the need for a heat source separate from the mold. It also eliminates the need to retract the heat source from the tube before applying the mold to the tube.
Thus, one aspect of applicants"" invention includes a mold for shaping the opening of a selected end region of a first, hollow, generally cylindrical glass tube, where the mold includes means for enabling the mold to function as a heat source for rendering the tube malleable so it can be shaped by the mold.
In one embodiment of the invention, the mold includes two elongated side pieces having inner surfaces designed to be applied around and along a selected end section of a cylindrical tube for shaping the selected end section of the cylindrical tube over a first distance from the end of the tube. The mold also includes an end plug having a cylindrical stub for insertion into the opening of the tube, at its selected end region, for shaping the rim and controlling the inner diameter of the cylindrical tube along a first distance from the end of the tube. One of the two elongated side pieces includes a gas distribution channel, formed within the side piece, for enabling the ejection of gas along an inner surface of the one side piece and an arrangement for coupling the gas distribution channel of the one elongated side piece to a source of gas for enabling the one side piece and the mold to function as a heat source.
Another aspect of the invention is directed to apparatus and method for shaping glass tubes incorporating a multi-piece mold of the invention. The apparatus includes a support means for holding the tube, other than at a selected region, and an actuatable mechanical holding means for holding the multi-piece mold in close proximity to the selected end region of the tube. The mold includes a heat source for supplying heat to the selected region of the tube for placing the selected region in a malleable state. When that condition is reached, the mold is applied to the selected region of the tube for shaping the selected end region of the tube to conform to the inner surfaces of the mold.
A method embodying the invention includes the steps of shaping the tube using the multi-piece mold embodying the invention and the apparatus for manufacturing the tube.
In one embodiment of the invention, a temperature sensing means controls the heat source and the application and retraction of the mold.